& 
392 - True AND Gries: Heavy METALS 
mitting growth was obtained for each of the salts of the lighter 
metals taken. This was necessary in order to get some idea of the 
permissible concentrations in which the latter might be used. 
Table II presents in brief the growth-rates made by the lupine 
roots in solutions of the salts of the second group of metals (and 
of urea). 
SIMPLE MIXTURES 
Knowing now the effect, on the growth-rate, of the heavy 
metals under study, also that of the salts of the lighter metals 
which were made use of, we have a basis for ascertaining the action 
of these compounds when their solutions are mixed. The method 
of procedure in this connection consisted briefly in mixing, with a 
series of graded solutions of the heavy metals, a definite quantity 
of the salts of the lighter metals. Two general classes of salts 
could be chosen for this purpose ; first, those in which a common 
anion occurs in combination with the different cations made use 
of; second, salts in which also the anions differed. By making 
up solutions molecularly, as was done in every case, a comparison 
of results obtained from the same cations, combined in the two 
ways indicated, would enable us to judge of the action of the anions. 
Table III summarizes growth-results obtained by growing 
lupine radicles in a series of solutions of copper salts mixed with 
salts of one lighter base in varying degrees of concentration. The 
growth-rates obtained are directly comparable to those resulting 
from the action of the simple solutions of the heavy metals. It 
will be noted that when copper sulphate is mixed with calcium 
sulphate, the latter containing mj/t44 grams per liter, a corre- 
sponding growth-rate is found in the case of the simple solution 
(Table II) at a concentration of copper sulphate indicated by 
m/65536, and in the case of the mixed solution (Table III) at 4 
concentration of 2/16384. These facts indicate that the presence 
of the given amount of calcium sulphate enables the plant to with- 
stand four times as much copper as it was able to withstand when 
the latter occurred in simple solution. A further inspection of the 
tables shows that when calcium sulphate is present in weaker solu- 
tions, the antagonizing action is still strong, even when calcium 
sulphate is present in a concentration of m/512. 
When to copper chloride, magnesium chloride is added in 4 
